1. Field of the Invention
The present invention relates to a multicast delivery control apparatus and method for content delivery using a multicast network.
2. Description of the Related Art
The multicast technique is effective in transmitting packets having the same content to a plurality of terminals. Receivers send to a router reception requests of multi cast address indicating content they want to receive, and the router generates a delivery tree. Content that is delivered to a multi cast address is copied, when necessary, at nodes of a network according to the delivery tree and is forwarded to receivers. Multicast delivery on an IP network is realized by using a multicast group management protocol such as internet group management protocol (IGMP) or multicast listener discovery (MLD) or a multicast routing protocol such as protocol independent multicast-sparse mode (PIM-SM).
Since the multicast is a technique capable of efficiently transmitting the same content to all receivers, it may be used in the form of a content broadcast for causing many receivers to simultaneously view a large amount of data such as multimedia content. However, there may be a case that it is effective to deliver, in accordance with their respective states, different pieces of content to receivers who sent the same reception request. For example, in ground-wave broadcast, news and weather forecasts suitable for respective receiver regions are delivered to those respective regions. If commercial messages that would attract each user (viewer) can be inferred correctly on the basis of his or her sex, age, etc. and delivered to him or her, advertisers are enabled to deliver effective advertisements and users need not view uninteresting advertisements. To cut the costs of such redundant delivery of content and allow the content provider side to form content structures flexibly, a mechanism is needed that allows the sender side to switch content to be received by each user. Another mechanism is also needed that enables efficient content switching in accordance with the profile of each of many users.
In the related art, a method for realizing such delivery with switching of multicast content in accordance with the profile of each user is such that users who want to have different pieces of content delivered are caused to join to different multicast addresses in advance and the pieces of content are delivered to those addresses. Another method is such that an instruction to change the reception channel is sent externally to each user terminal as appropriate.
Related prior art references are:                JP-A-2002-314599        JP-A-2002-314600        RFC2236 Internet Group Management Protocol, Version 2        FRC2710 Multicast Listener Discovery (MLD) for IPv6        RFC2362 Protocol Independent Multicast-Sparse Mode (PIM-SM)        
However, the method that users who want to have different pieces of content delivered are caused to join to different multicast addresses in advance is not flexible because it is necessary to determine a delivery schedule before opening the multicast addresses to the users. Further, to deliver the same content to users who are members of different multicast addresses, a problem arises a sender must send multicast packets to the respective groups.
A method that a reception multicast address conversion instruction is issued to each client has the following problem.
First, every client needs to introduce software that has a function of generating an IGMP or MLD packet according to the received instruction and transmitting it: a software introduction cost and a terminal processing cost at the time of conversion are incurred. Where authentication is performed on a multicast address basis, an authentication process needs to be executed, though in the same authorization unit, every time content switching is performed, which increases the overhead.
Where authentication is not performed, a receiver is rendered in a receivable state only if he or she sends a request to join a group. Therefore, if a conversion instruction to a client is disregarded because of network trouble or by intention of a receiver, it is unavoidable that the receiver receives content that is not intended by a content provider.